The invention relates to an electronically commutated DC motor having an air gap in which a stator coil is arranged and having a first permanent magnet rotor arranged on one side of this air gap. A second permanent magnetic rotor is positioned at the opposite side of the air gap, whereby the second rotor is coaxially arranged to the first rotor without a mechanical connection to the first rotor.
From DE 195 03 521 A1 an electronically commutated drive motor with planar air gap having a fan wheel connected to the rotor is known. Such motors are relatively inexpensive because of their simple construction and are therefore used, among other applications, also in the interior of motor vehicles. However, a certain noise level may not be surpassed in these situations. It is therefore important that the rotor of the fan wheel will not begin to vibrate as a result of the occurring driving accelerations but remains secured within its guide bearing. The required axial force is provided by magnetic coupling between the rotor magnet and the steel disk positioned within the stator. A disadvantage is that eddy currents will result which decrease the efficiency of the motor and indirectly increase the running noise level. A further disadvantage of such disk rotor motors is that, in general, electromagnetically caused axial reaction forces result which may cause the entire system to vibrate.
It is an object of the invention to provide an electric motor of the aforementioned kind which has an even more reduced noise level at acceptable costs.